The present invention is a process for separating methyltrichlorosilane from dimethyldichlorosilane in a mixture. The process comprises contacting a mixture comprising methyltrichlorosilane and dimethyldichlorosilane with activated carbon, where the methyltrichlorosilane is selectively adsorbed by the activated carbon. The process allows for the recovery of a dimethyldichlorosilane fraction reduced in methyltrichlorosilane concentration. The methyltrichlorosilane can be recovered by desorption from the activated carbon. The present process is especially useful for removing low levels of methyltrichlorosilane from dimethyldichlorosilane.
The commercial production of methylchlorosilanes involves the contact of methyl chloride with silicon metalloid in the presence of a catalyst comprising copper at temperatures within a range of about 300.degree. C. to 350.degree. C. Typically this process is optimized for the production of dimethyldichlorosilane, with lessor amounts of methylsilanes, methylchlorosilanes, methylhydrosilanes, C.sub.2 to C.sub.7 hydrocarbons, polysilanes, polysiloxanes, silylmethylenes, and other species being formed. This product mixture usually undergoes a series of process steps such as distillation, condensation, and the like to effect separation and recovery of commercially important individual components of the product mixture. However, standard separation techniques based on the difference in the boiling point between compounds become difficult and expensive when the compounds have similar boiling points. This situation exists with the separation of methyltrichlorosilane (b.p. 66.1.degree. C.) and dimethyldichlorosilane (b.p. 70.1.degree. C.). The present inventors have found that activated carbon selectively adsorbs methyltrichlorosilane when in mixture with dimethyldichlorosilane and therefore provides an alternative method for separation of these two methylchlorosilanes. The present process has been found particularly effective for removing trace amounts of methyltrichlorosilane from dimethyldichlorosilane, thereby providing dimethyldichlorosilane essentially free of methyltrichlorosilane contamination.
Wilkman et al., U.S. Pat. No. 5,290,342, describe a process for separating ethylsilane from silane by selective adsorption of the ethylsilane onto activated carbon.
Bothe et al., U.S. Pat. No. 5,445,742, describe a process for purification of halosilanes. The process consists of contacting a mixture comprising a halosilane and a hydrocarbon with an adsorbent selective for the hydrocarbon. Examples of useful adsorbents taught by Bothe et al. include activated carbon, carbon molecular sieves, and high silica zeolite.
The cited art does not recognize that activated carbon can be used as a selective adsorbent to separate methyltrichlorosilane from dimethyldichlorosilane.